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Crop Improvement > Inheritance Studies

Inheritance Studies

Ayyangar and Nambiar, (1935): Studies in Dolichos lablab.

This study showed that a monohybrid ratio for downward versus upward hairs on the internodes and the gene was symbolized as H. A similar type of ratio was found for medium-broad and narrow-pod width and the factor for this character was named as W. The same authors found monohybrid (3:1) and dihybrid (15:1) ratios for erect and drooping pods; the genes involved here were designated as E1 and E2. They also observed (1935 b and 1936) different seed coat colours in Dolichos lablab, viz., black, chocolate, khaki and buff and found monohybrid and dihybrid ratios in crosses between varieties with different seed coat colours.

While this study shows that the directions of hairs and pod width are each caused by a single factor; the position of pod was found to be due to duplicate genes. The study of the joint segregation reported here shows that the factors for hair direction (H), pod width (W), pod position (E1, E2) and seed colour (C) were independent and showed no linkage. Pod width and seed shape and also pod position and pod surface did not show any recombination which may be due to pleotropic action of a single gene or very close linkage of the factor controlling these characters. However, the populations of just 752 F2 plants studied here do not appear to be large enough to allow a clear choice between these alternative explanations.

From the inheritance studies reported here, it is found that the characters of type-21 are dominant over those of type–3. The genetic constitution of the two types, therefore, may be represented as HH WW E1E1 E2 E2 CC for type 21 and hh ww e1 e1 e2 cc for type –3 respectively.

Patil and Chavan, (1961): Inheritance of some characters in Field bean.

Inheritance of a number of characters in this species was studied. Now two varieties, D.L. 259 and CO.12 were crossed in 1960. D.L.259 had green and flat pods and seeds were chocolate colour. Whereas in CO.12, these characters were light- green bloated and brown. F1 hybrids were sown in 1961. F2 populations consisting of 397 individuals were studied in 1962 and the performance of 36 families in the F3 generation was recorded in 1963.

In respect of pod colour, pod shape and seed colour a 3:1 ratio was obtained. This explained the fact that in each segregation a single gene was involved. Green pod colour was dominant over light green, flat pod shape over bloated and chocolate seed colour over brown. Three different and independent genes were, therefore, responsible for these three characters. Pigmentation in the vegetative plant parts was found to be dominant over light– green.

D’Cruz and Ponnaiya, (1968) Inheritance of pod and seed colour and pod shape in garden bean.

Ayyangar and Nambiar (1935, 1941) reported on the genetic behavior of pod and seed colour and isolated eight pigmented types in Dolichos lablab L. Later, Patil and Chavan (1961) also studied the inheritance of a number of characters in that species. Now two varieties, D.L. 259 and CO.12 were crossed in 1960. D.L.259 had green and flat pods and seeds were chocolate colour. Whereas in CO.12, these characters were light- green bloated and brown. F1 hybrids were sown in 1961. F2 populations consisting of 397 individuals were studied in 1962 and the performance of 36 families in the F3 generation was recorded in 1963.

In respect of pod colour, pod shape and seed colour a 3:1 ratio was obtained. This explained the fact that in each segregation a single gene was involved. Green pod colour was dominant over light green, flat pod shape over bloated and chocolate seed colour over brown. Three different and independent genes were, therefore, responsible for these three characters.

Pigmentation in the vegetative plant parts was found to be dominant over light– green. Whereas, Ayyangar and Nambiar (1935) reported the involvement of four genetic factors. However, the gene involved in this segregation has been symbolized as Grp. The single gene responsible for pod shape has been designated as Fp. and for seed colour gene symbol suggested was Csc.

Manjunath et al., (1973): Anthocyanin genetics of Dolichos.

Hybridization was done between a local strain of Dolichos lablab (L.) var. lignosus Prain and a local strain of D. lablab var. typicus Prain. The former has no anthocyanin pigment in any part of the plant body, whereas the latter has pigmentation in different parts including node, internode and pod. The F1, F2 and F3 generations of this cross were grown and plants were scored for pigmented and non-pigmented character.

The presence of pigment in the node, internode and pod of F1 and a 27: 37 ratio of pigmented to non-pigmented scored in F2 for all the three characters reveals that pigmentation in each of the plant parts–node, internode and pod–is governed by three complementary genes (A, B and C). This is confirmed by the breeding behaviour of 60 F3 families. The joint segregation of character pairs revealed no recombinants whatsoever, i.e., there was no segregants with pigmentation in any one or two of these three plant parts without pigmentation in the remaining part (s), thus leading to conclusion that the same set of genes (A, B and C) is governing anthocyanin pigmentation in all the three plant parts.

Though the joint segregations of the character pairs revealed no recombinant types, it cannot be ruled out that the pleiotropic action of the genes A, B and C might be only an apparent one resulting due to the close linkage among different genes governing each of the three characters.

The F1 and F2 populations of the above crosses were raised at Punjabrao Krishi Vidyapeeth, Akola during Kharif 1977. The spacing of 90 x 60 cm was maintained. The observations on stem colour, calyx colour and pod shape of parents and F1S were recorded. In F2 the segregation of three characters was recorded in all the four crosses. The X2 test was used to test the goodness of fit of the observed frequencies of the characters.

The mode of inheritance of stem colour in ail the four crosses was found to be digenic. In a cross between No. 682 x Surti No. 3, both the parents were white and F1 had the light green colour indicating that the genes present in both the parents compliment to each other and produced the light green colour. The F2 segregation was 9 light green : 7 white.

In other three crosses the F2 segregation showed 13 : 3 ratio. In a cross between No. 682 x Chapatwal, red colour of Chapatwal was inhibited by the white stem colour of No. 682, while in New Dharwar x Chapatwal, red colour of stem was inhibited by green. The green colour was inhibited by light green in a cross between Surti No. 3 x New Dharwar.

The calyx colour in crosses between No. 682 x Surti No. 3 and No. 682 x Chapatwal showed 9:7 segregation ratio. In both the crosses, green was dominant in F1. In the crosses between New Dharwar x Chapatwal and Surti No. 3 x New Dharwar, violet was dominant to light purple and light green to violet respectively and favoured the hypothesis of monogenic inheritance (3 : 1).

The length of pod was found to be controlled by two genes in crosses between No. 682 x Surti No. 3, No. 682 x Chapatwal and gave 9 : 7 complementary ratio. In other two crosses viz., New Dharwar x Chapatwal and Surti No. 3 x New Dharwar, the F2 showed the mendelian segregation of 3: 1.

Prasanthi, (2005): Inheritance of photo– insensitivity.

It was observed that local land – races are photosensitive and take about 120 –125 days for flowering. To study photoperiod sensitivity, varieties Hebbal Avare-3 and land races were grown in kharif 2000. Hebbal Avare flowered within 45–50 days after sowing, while local landraces came to flowering 125 days after sowing in the first week of November 2000.

Two crosses between landraces of Andhra Pradesh and HA 3 of Karnataka were made during kharif 2000 and F1 plants were grown in kharif 2001. All of them flowered. F2 plants were sown in May 2002 and data on flowering pattern was recorded. This showed the dominance of photo–sensitivity and the segregation between photo–sensitivity and photo-insensitivity was in the ratio of 3:1, thus indicating that this character has bean governed by a single pair of genes.

Dolichos bean Lablab purpureus L. Sweet is one of the multipurpose legumes, used as a cosmopolitan crop around the world. The crop is mainly grown for its green pods, used as vegetables while the dry seeds are used as dhal making. It is one of the major sources of protein as dietary in southern India. Its productivity is low 228 kg/ha and its nature of photo insensitivity resulted hindrance in the Dolichos bean improvement. To break the yield barrier, inheritance study of qualitative character along with quantitative character is important. In this context, inheritance and interrelationships for five qualitative characters viz., growth habit, color of leaf, leaf structure, pod curvature and fragrance in a cross of GL 153 x HA 4 were studied. Inheritance revealed the complementary gene interaction (9 : 7) for leaf structure. Whereas, growth habit and color of leaf were controlled by three genes (39: 25)- a one basic gene, one inhibitory gene and one anti-inhibitory gene governing this character. The pod curvature and fragrance/aroma were governed by four genes with a ratio 117: 139 revealing that two complementary genes, one inhibitory and one anti-inhibitory gene were involved in these characters. In the reciprocal cross(HA 4 x GL 153) inheritance revealed that one basic independent and two complementary genes (57 : 7) for growth habit, color of leaf and leaf structure were controlled by three complementary genes (54:10). Four genes controlling pod curvature (195 : 61) indicate two duplicate, one inhibitory and one anti-inhibitory gene governing this character. Fragrance/aroma was governed by two genes with a ration 13 : 3 revealing that one inhibitory gene was involved in this characters. From the study it reveals growth habit was governed by three genes GH1, and GH2 act as GH1 and GH3 act as GHAI. Whereas leaf color inherited by three genes basic gene DG1, DG2 act as DG1 and DG3 act as DgAI. While leaf structure was governed by three genes Ls1, Ls2, and Ls3 act as Ls1 or Ls2. Pod curvature was governed by four genes PC1, PC2, PC1 and PCAI. Fragrance was governed by three genes S1, SAI, S1 act as S1 and S2 act as SAI. Joint segregation revealed that there was no linkage exists among characters. All the characters were segregating independently. These different genetic ratio of direct and reciprocal cross was due to characters governed by duplicate genes. Multiple alleles, genetic and cytoplasmic effects, maternal effects and their interactions.

The nature and magnitude of genetic variance for yield and its component traits were studied in Indian bean using diallel analysis. The estimates of general combining ability (GCA) variance were much higher than specific combining ability (SCA) variance except days to 50% flowering, number of pod per cluster and fiber content; this indicated the importance of both additive as well as non-additive gene effects are involved in the expression of these characters. Genotypes NIB-69 and NIB-54 were identified as good general combiner for pod yield per plant. The cross combination viz., NIB-57 x NIB-69, NIB-69 x NIB-80, NIB-32 x NIB-54, NIB-41 x NIB-69 and NIB-23 x NIB-54 were the most promising crosses for improvement of pod yield. In the light of present study, the use of good general combining parents in the hybridization programme, selection of the desirable segregants from the segregating generations by adopting progeny selection method for exploiting additive genetic variance would lead to rapid improvement in this crop.

To our knowledge, detection of linkage and its phase and estimation of recombination fraction and distance between genes controlling photoperiodic response to flowering time and growth habit reported in the present study is first of its kind in dolichos bean. The strong linkage in coupling phase suggests effectiveness of selection for PIS plants in breeding populations using growth habit as a surrogate, as the latter is easily observable/assayable under field conditions. Also, relatively small-sized F2 populations will suffice to recover and select PIS plants with determinate growth habit. Cultivars with PIS and D growth habit are desirable from farmer's point of view, as they facilitate high density planting and hence help maximize productivity of Dolichos bean.

Gradual shift in onset of monsoon driven by climate change, has forced farmers to unpredictably delay the sowing to match the crop growth period to distribution of rainfall. Sowing date is one of the most important factors which have tremendous effect on biological yield of a crop species. This is specifically true in highly photoperiod sensitive crops such as Dolichos bean. Theoretical considerations and farmers' belief are in favour of photoperiod sensitive cultivars under delayed sowing environments. The photoperiod sensitive (PS) and photoperiod insensitive (PIS) genotypes were planted during August, September and October months (representing delayed sowing environments) in randomised block design in two replications. The data were recorded on days to 50% flowering, primary branches plant-1 and fresh pod yield plant-1. The performance stability of five PS and five PIS Dolichos bean grown in delayed sowing dates was compared based on three criteria namely per se performance, regression (bi) of environment indices on crop response and deviation from regression (s2di) to examine theoretical consideration and farmers' belief. The per se performance of PS genotypes was superior to PIS genotypes although they displayed greater sensitivity (bi>1) to sowing date environments. On the other hand, performance of PIS genotypes was lower than that of PS genotypes but displayed least sensitivity (b = 1) and higher stability (S2di non-significant) to sowing date environments. If farmer choose PS/PIS cultivars, they need to be planted not later than September to harness their complete genetic potential. The study provided preliminary evidence to support theoretical hypotheses and farmers experience-based view that PS cultivars perform better across delayed sowing date environments although they may not be as stable as PIS cultivars.

An understanding of the effect of environmental cues, especially photoperiod and temperature on time to flowering, and the genetics of photoperiod-induced sensitivity to flowering time (PSFT), growth habit (GH), floral and pod traits help enhance the pace and efficiency of breeding dolichos bean, a photoperiod sensitive (PS) short-day grain legume species. A series of experiments carried out at the experimental plots of the Department of Genetics and Plant Breeding, University of Agricultural Sciences, Bengaluru during 2012-2015 revealed the greater role of temperature than photoperiod in regulating time to flowering of PS genotypes. Dolichos bean requires critical minimum and maximum photoperiod of 11.11hrs and 12.28hrs, respectively for time to flowering. While, PSFT and flower color (FC) are each controlled by bi-allelic monogenic locus, GH, pod curvature (PC) and raceme emergence (RE) are each controlled by two genes with classical complementary and inhibitory epistasis, respectively. The genes controlling GH, PSFT and RE are linked with recombination fractions and map distances of 0.24 and 33.61cM between PSFT and GH, 0.35 and 61.40cM between PSFT and RE and 0.31 and 49.43cM between GH and RE. Higher amino acid sequence homology of dolichos bean homologues (LpLFY, LpFKF1, LpLHY and LpTFL1) of Arabidopsis PSFT candidate genes (LFY, FKF1 and LHY) and GH candidate gene (TFL1) with those of soybean, common bean and Medicago and cleaved amplified polymorphic sequences assay indicated possible similar genetic and physiological mechanisms controlling PSFT and GH. The results did not favour ignoring epistasis in studies designed for determining the relative magnitude of additive and dominance genetic variances controlling the target traits. The study also revealed preferential use of parents contrasting for general combining ability and/or with intermediate genetic divergence to maximise the frequency of heterotic hybrids, the use of which is likely to result in greater chances of recovering high yielding purelines.

The choice of suitable selection strategy for genetic improvement of any crop species hinges on the relative contribution of additive and non-additive components of genotypic variation of economic traits. Simplified triple test cross (STTC) design was used to detect epistasis and assess epistasis-driven bias in the estimates of additive (ɑ2A) and dominance (ɑ2D) components of genotypic variation of economic traits in Dolichos bean. The material for the study consisted of 12 genetically diverse inbred lines and two pairs of testers contrasting for economic traits. The 12 inbred lines were crossed to two pairs of testers in 2012 rainy season to generate two sets of STTC progenies, which were evaluated in 2013 and 2014 rainy season at the University of Agricultural Sciences, Bengaluru, India. The results indicated an important role of epistasis in inheritance of all the traits in Dolichos bean. While ɑ2A predominated in the inheritance of racemes/ plant, ɑ2D predominated in the inheritance of pod weight/plant. Only ɑ2A was important in the inheritance of days to flowering and seed weight/plant. The 12 inbred lines used in the study contributed significantly to varying extent to epistasis governing different traits in both sets of STTC progenies in both years. The bias in the estimates of ɑ2A was greater than that in the estimates of ɑ2D. Therefore, it is not advisable to ignore epistasis in studies designed for determining the relative magnitude of ɑ2A and ɑ2D controlling target traits in Dolichos bean.

Keerthi, et al. (2016): Further evidence for the genetic basis of qualitative traits and their linkage relationships in dolichos bean (Lablab purpureus L.).

An investigation on inheritance of qualitative traits in dolichos bean revealed biallelic monogenic control of photoperiodinduced sensitivity to flowering time and flower colour in F2 and F3 generations. While, growth habit and pod curvature are each controlled by two genes that exhibit classical complementary epistasis, raceme emergence was controlled by two genes that displayed classical inhibitory epistasis. The dominant alleles, at two different unlinked pairs of genes are necessary for plants to exhibit indeterminate growth habit and bear straight pods. Any other combination of alleles at the two pairs of genes result in plants displaying determinate growth habit and bearing curved pods. While, the genes controlling growth habit, PSFT and raceme emergence are linked. Those controlling flower colour and pod curvature are segregated independent of each other. These results are discussed in relation to strategies for breeding dolichos bean.